Copending Application U.S. application Ser. No. 10/834,722 pending, filed Apr. 29, 2004, entitled “Reimageable Medium”, with the named inventors, Gabriel Iftime, Naveen Chopra, Peter M. Kazmaier, the disclosure of which is totally incorporated herein by reference, discloses a reimageable medium composed of: a substrate; and a photochromic material, wherein the medium is capable of exhibiting a color contrast and an absence of the color contrast, wherein the medium has a characteristic that when the medium exhibits the absence of the color contrast and is then exposed to an imaging light corresponding to a predetermined image to result in an exposed region and a non-exposed region, the color contrast is present between the exposed region and the non-exposed region to form a temporary image corresponding to the predetermined image that is visible for a visible time, wherein the medium has a characteristic that when the temporary image is exposed to an indoor ambient condition for an image erasing time, the color contrast changes to the absence of the color contrast to erase the temporary image in any of the following: (i) when the indoor ambient condition includes darkness at ambient temperature, (ii) when the indoor ambient condition includes indoor ambient light at ambient temperature, and (iii) when the indoor ambient condition includes both the darkness at ambient temperature and the indoor ambient light at ambient temperature, and wherein the medium is capable of undergoing multiple cycles of temporary image formation and temporary image erasure.
Copending Application U.S. application Ser. No. 10/835,518 pending, filed Apr. 29, 2004, entitled “Method for Forming Temporary Image”, with the named inventors, Peter M. Kazmaier and Gabriel Iftime, the disclosure of which is totally incorporated herein by reference, discloses an image forming method composed of: (a) providing a reimageable medium composed of a substrate and a photochromic material, wherein the medium is capable of exhibiting a color contrast and an absence of the color contrast; (b) exposing the medium to an imaging light corresponding to a predetermined image to result in an exposed region and a non-exposed region, wherein the color contrast is present between the exposed region and the non-exposed region to allow a temporary image corresponding to the predetermined image to be visible for a visible time; (c) subjecting the temporary image to an indoor ambient condition for an image erasing time to change the color contrast to the absence of the color contrast to erase the temporary image without using an image erasure device; and (d) optionally repeating procedures (b) and (c) a number of times to result in the medium undergoing a number of additional cycles of temporary image formation and temporary image erasure.
Copending Application U.S. application Ser. No. 10/834,529 pending, filed, Apr. 29, 2004 entitled “Reimageable Medium With Light Absorbing Material”, with the named inventors, Gabriel Iftime, Peter M. Kazmaier, James Mayo and Paul Smith, the disclosure of which is totally incorporated herein by reference, discloses a reimageable medium for receiving an imaging light having a predetermined wavelength, the medium composed of: a substrate; a photochromic material capable of reversibly converting among a number of different forms, wherein one form has an absorption spectrum that overlaps with the predetermined wavelength scope; and a light absorbing material exhibiting a light absorption band with an absorption peak, wherein the light absorption band overlaps with the absorption spectrum of the one form.
1. Technical Field
The description set forth herein relates generally to a reimageable medium. More particularly, the description relates to a reimageable medium having a dual-layered structure that prevents noticeable coloration from ambient ultraviolet light.
2. Description of Related Art
Many paper documents are promptly discarded after being read. Although paper is inexpensive, the quantity of discarded paper documents is enormous and the disposal of these discarded paper documents raises significant cost and environmental issues. One solution to address this problems is the use of temporary documents or reimageable paper as described in the following documents: (1) Henri Bouas-Laurent et al., “Organic Photochromism,” Pure Appl. Chem., Vol. 73, No. 4, pp. 639-665 (2001); (2) Martin et al., U.S. Pat. No. 5,710,420; (3) McCue et al., U.S. Pat. No. 6,500,245 B1; (4) Japanese Laid Open Patent Document No. 2003-131339 (“Reversible Image Display Medium, Method and Device”); (5) H. Hattori et al., “Development of Paper-like Rewritable Recording Media and Systems,” Asia Display/IDW '01, pp. 15-18 (2001); (6) Saeva, U.S. Pat. No. 3,961,948; (7) Foucher et al., U.S. Pat. No. 6,358,655 B1; and (8) Foucher et al., U.S. Pat. No. 6,365,312.
Reimageable paper contains a written image, which can then be erased, allowing the paper to be re-written with a new image. For example, photochromic self-erasing, reimageable paper may be written by using ultraviolet (UV) light of about 365 nm wavelength. This allows printed information to be readable by ultraviolet light and visible light for a predetermined period of time, for example, 4 hours. After an extended period of time, for example, 20 hours, the printed information is self-erasing, leaving a blank document ready to be reimaged with new information. Because light is used both for writing (UV), as well as for reading the document (UV and visible including room-light from a bulb or sun-light), unimaged areas of the document are sensitive to the UV component of the reading light. Unimaged areas become colored after a period of time in turn reducing the contrast between the white and colored states. The lack of contrast minimizes and produces poor readability of the document.
One solution to reduce the background coloration, for example, the coloration of the unimaged areas, of temporary documents may be to use a switchable protective photochromic material overcoated onto a writing or imaging layer. However, the intermixing of the overcoating and writing layers may result in poor coverage, and non-uniform protection. Additionally, the presence of a UV absorbing protective layer may reduce the UV writing efficiency on the imaging layer itself, thereby causing the written areas to be faint in color, and quick to fade under intense sunlight. A similar result may be seen when using a multilayer coating, for example, an absorbing protecting layer over an imaging layer.
Accordingly a need exists for a transient document which is reimageable and self-erasing that provides superior writeability and stability against exposure to ultraviolet light.